I have a client who is interested in using a new frame, made from e.white pine, but making it look as if it's 200 years old. Besides distressing the surface and adding a few unnecessary mortises in various locations, does anyone have any ideas about coloring or staining pine to resemble naturally aged beams?

try a mixture of ground pumice, linseed oil and dry gray clay on a sample to see if your like the result.
apply with double O steel wool.
lots of elbow grease required.
OR
add the scorched look with a carefully applied blow torch
OR
a mixture of iron oxied and linseed oil applied with double O steelwool
OR
some strong hot tea (staining)
OR
any of the above in any combination.
All are non destructive to the wood.
Have fun.

pardon the misspellings in the previous
meant to say
YOU instead of your
OXIDE instead of oxied
old fingers and this keyboard don't spell well